The structure and chemical reactions of highly strained organic molecules will be explored with ab initio molecular orbital methods. Of particular interest are cyclic allenes, alkynes, and cumulenes. Study of the potential surfaces for reactions photochemical reaction that may involve this remarkable intermediate. Homodesmic and isodesmic reactions will be used to estimate strain in the homologous series of cyclic allenes and butatrienes. We will study novel cycloadditions or rearrangements that might involve strained allenes, butatrienes and pentatetraenes. In most cases, these ab initio calculations will be used to guide concurrent experimental studies.